Geoscience Frontiers 6 (2015) 437e451

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Research paper

Geochemistry and petrogenesis of Rajahmundry trap basaltsof Krishna-Godavari Basin, India

C. Manikyamba a,*, Sohini Ganguly b, M. Santosh c, Abhishek Saha a, G. Lakshminarayana d

aCSIR-National Geophysical Research Institute, Hyderabad 500 007, IndiabDepartment of Geology, University of Calcutta, 35, B. C. Road, Kolkata, 700 019, Indiac School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, ChinadMidwest Group, Banjara Hills, Hyderabad 500 034, India

a r t i c l e i n f o

Article history:Received 26 February 2014Received in revised form20 May 2014Accepted 22 May 2014Available online 13 June 2014

Keywords:Rajahmundry Trap Basalts (RTB)Fault-controlled fissuresFractional crystallizationEnriched mantle sourcePlume-lithosphere interaction

* Corresponding author. Tel.: þ91 (0)40 27012625,fax: þ91 (0)40 27171564.E-mail address: cmaningri@gmail.com (C. Manikyamb

Peer-review under responsibility of China University

http://dx.doi.org/10.1016/j.gsf.2014.05.0031674-9871/� 2015, China University of Geosciences (

a b s t r a c t

The Rajahmundry Trap Basalts (RTB) are erupted through fault-controlled fissures in the Krishna-God-avari Basin (K-G Basin) of Godavari Triple Junction, occurring as a unique outcrop sandwiched betweenCretaceous and Tertiary sediments along the east coast of India. Detailed geochemical studies haverevealed that RTB are mid-Ti (1.74e1.92) to high-Ti (2.04e2.81) basalts with a distinct quartz tholeiiticparentage. MgO (6.2e13.12 wt.%), Mg# (29e50) and Zr (109e202 ppm) suggest that these basalts evolvedby fractional crystallization during the ascent of the parent magma along deep-seated fractures. Mod-erate to high fractionation of HREE, as indicated by (Gd/Yb)N ratios (1.71e2.31) of RTB, suggest theirgeneration through 3e5% melting of a Fe-rich mantle corresponding to the stability fields of spinel andgarnet peridotite at depths of 60e100 km. Low K2O/P2O5 (0.26e1.26), high TiO2/P2O5 (6.74e16.79), La/Nb(0.89e1.45), Nb/Th > 8 (8.35e13), negative anomalies at Rb reflect minimum contamination by graniticcontinental crust. (Nb/La)PM ratios (0.66e1.1) of RTB are attributed to endogenic contamination resultedthrough recycling of subducted oceanic slab into the mantle. Pronounced Ba enrichment with relativedepletion in Rb indicates assimilation of Infra- and Inter-trappean sediments of estuarine to shallowmarine character. Geochemical compositions such as Al2O3/TiO2 (3.88e6.83), medium to high TiO2 (1.74e2.81 wt.%), positive Nb anomalies and LREE enrichment of these RTB attest to their mantle plume originand indicate the generation of parent magma from a plume-related enriched mantle source with EM Isignature. Ba/Th (46e247), Ba/La (3.96e28.51) and Th/Nb (0.08e0.13) ratios suggest that the sourceenrichment process was marked by recycling of subduction-processed oceanic crust and lithosphericcomponents into the mantle. Zr/Hf (37e41) and Zr/Ba (0.51e3.24) indicate involvement of an astheno-spheric mantle source. The Rajahmundry basalts show affinity towards FOZO (focal zone mantle) andPSCL (post-Archaean subcontinental lithosphere) which reflect mixing between asthenospheric andlithospheric mantle components in their source. Origin of RTB magma is attributed to plume-lithosphereinteraction and the upward movement of melt is facilitated by intrabasinal deep-seated faults in the K-GBasin.

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1. Introduction

The late Cretaceouseearly Tertiary Rajahmundry Trap Basalts(RTB) of the Krishna-Godavari Basin extends w60 km on eitherside of the Godavari River, north of the city of Rajahmundry inAndhra Pradesh, India (Baksi et al., 1994; Baksi, 2001; Sen andSabale, 2011). The RTB have been considered as the eastwardcontinuation of Deccan Traps thus representing an example oflong distance lava transport spanning over 1500 km across Indiaand about 70 km into the Bay of Bengal (Jay, 2005; Jay and

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Widdowson, 2008; Keller et al., 2008; Self et al., 2008). Thesetraps are the only known outcrops of basalt flows along the eastcoast of India, coeval with the Deccan Traps. Recent work byLakshminarayana et al. (2010) has brought to light the stratigraphicframework, flow morphology and volcanological features of theRajahmundry Trap lava flows. In quarries of the Pangidi-Rajahmundry area, three distinct basalt flows interbedded withtwo Intertrappean sedimentary horizons are observed, which are inturn underlain by the late Cretaceous fossiliferous limestone bed(Infratrappean) and overlain by the Cenozoic Rajahmundry Forma-tion (conglomerate/sandstone). The fossiliferous Infratrappean bedrepresents amarker zoneofK-Pg (CretaceousePaleogene) boundarymass extinction. Ar-Ar geochronological data have established thatthe RTB (w64 Ma) are contemporaneous with the Deccan Traps(65e66Ma) that records voluminous volcanic activity on the Indiansubcontinent marking the catastrophic events at K-T boundary(Baksi et al., 1994; Allegre et al., 1999; Pande et al., 2004; Sheth,2005). However, detailed petrological and geochemical studies ofthe RTB are lacking till date to appraise their genesis and mode ofemplacement. This paper presents new geochemical (major, traceand rare earth elements) data for the RTB in order to elucidate (i) thepetrogenetic processes associated with their evolution and (ii) im-plications on their emplacement in terms of regional tectonicframework.

2. Geological setting

The RTB are located along the southeastern part of the GodavariTriple Junction (Fig. 1A). The NWeSE trending Godavari Rift and theNNEeSSW to NEeSW oriented K-G Basin represents a tectonicjunction known as Godavari Triple Junction. This terrane preserves ageological record spanning Mesoproterozoic to Neogene and pro-vides evidences for Gondwana break-up, Cretaceous continentalriftinganddrifting (Lakshminarayana,1996, 2002; Lakshminarayanaet al., 2010). A series of NEeSW trending mounds present betweenDuddukuru and Rajahmundry, covering an area of w100 km2,represent theRTB (Fig.1A) in theKrishna-GodavariBasin (K-GBasin).The development of K-G Basin has been controlled by a phase-wiseuplift of the basement (Eastern Ghat Mobile belt) during Phanero-zoic. Lakshminarayana (1995a) suggested that a series of NEeSWstep faults controlled the development of east coast basins sinceMesozoic. From west to east, these blocks are the Mailaram high,Dammapeta Basin, Raghavapuram Basin and Pangidi-RajahmundryBasin (Fig. 1A). The Mailaram high was uplifted first during earlyMesozoic and controlled the sedimentation pattern in the Dam-mapeta Basin. Due to post Jurassic uplift, theMailaram high becamea watershed and resulted in the development of short headed fandelta streams flowing towards east (Lakshminarayana, 1997) for thefirst time. RTB is exposed in three separate areas, namely Nallajerla,Pangidi and Rajahmundry separated by younger sediments (GSI,1996). The occurrence of prominent outcrops is recorded in Pan-gidi andRajahmundryand the Rajahmundry Trap lavaflowsoccur asa single unit (Lakshminarayana, 1995b). The Pangidi-Rajahmundryarea of K-G Basin exposes coastal Gondwana sediments (Creta-ceous), RTB (K-Pg boundary), Rajahmundry Formation (Paleogene)and the Quaternary sediments (Table 1) (Fig. 1B). The uppermosthorizonsof theTirupati Formation, forming thebasementof theRTB,are represented by sandstone, clay and limestone and are known asthe ‘Infratrappean beds’ which in turn are unconformably overlainby the RTB (Lakshminarayana et al.,1992). The RTB are bounded by aprominent NEeSW fault along the northwestern margin and over-lain by the Cenozoic Rajahmundry Formation and Quaternary sedi-ments in the east. NWeSE lineaments/faults traverse the traps atDuddukuru and Pangidi (Fig. 1B). The entire succession of RTB ispreserved between these two faults.

Our present work deals with thewell-exposed succession of RTBfrom the Gowripatnam (17�1055.800N, 81�3704100E) and Duddukuru(17�202.200N, 81�35033.300E) quarries, located west of the Godavaririver. The RTB units here comprise of three distinct basaltic lavaflows (lower, middle and upper) separated by two Intertrappeansedimentary horizons identified as Intertrappean I and II. The20e30 m thick lower flow unconformably overlies theMaastrichtian-Danian Infratrappean bed (Fig. 2A). The lower basaltflow is characterized by the presence of physical volcanologicalfeatures such as rootless cones, tumuli and dyke like forms alongwith prominent development of single to multi-tier columnar(Fig. 2B) and radial jointing (Fig. 2C). Intertrappean I consists ofw2e3.5 m thick clay, marl and limestone intercalations which issandwiched between the lower and middle flows of RTB (Fig. 2A).Several invertebrate fossils have been collected from this limestonehorizon at Pangidi and Rajahmundry areas and this palae-ontological evidence has received great attention in view of theirsimilarity with the Intertrappean beds of western and central India(Lakshminarayana et al., 2010; Malarkodi et al., 2010). The middleflow represents 6e10m thick, greenish grey vesicular basalt restingunconformably over the clay and limestone of Intertrappean I. Thisflow is 1e2 m thick and appears to be massive. The middle flow isoverlain by Intertrappean II which is made of red clay/red bole. Theupper flow (5e17 m thick) unconformably overlies the Inter-trappean II and is made of fine-grained vesicular basalt.

3. Petrography

The lower, middle and upper flows of RTB are characterized byphenocrysts of plagioclase and clinopyroxene. Groundmass isgenerally marked by tiny plagioclase, granular pyroxene, opaqueminerals and glass. Plagioclase phenocrysts are dominant and aremostly lath-shaped (Fig. 3A). Clinopyroxene phenocrysts aremostlyprismatic and occur as individual medium-sized subhedral grains,and clusters of microphenocrysts. These clustered clinopyroxenemicrophenocrysts have been designated as tecoblast (Pattanayakand Srivastava, 1999; Ganguly et al., 2012). Euhedral olivine phe-nocrysts are minor and are partially or completely altered to pal-agonite and iddingsite. These are secondary constituents derivedmostly by the hydrous alteration of the primarymafic minerals. Thelower and middle flows exhibit vesiculation features containingabundant vug infillings and a greater proportion of groundmassglass, whereas the upper flow is massive with lesser vesicles.Devitrification is also observed at some places. The overall texturalpattern is intersertal and intergranular (Fig. 3B). Distinct develop-ment of clustered plagioclase phenocrysts represents glomer-oporphyritic texture (Fig. 3A). Some sections have the presence ofsecondary carbonates.

4. Analytical techniques

Least altered samples of trap basalts, collected from three lavaflows, were selected for detailed geochemical studies. Forty-twosamples were analyzed for major, trace and rare earth elementalcompositions. Rocks were powdered using an agate mortar. Majorelements were analyzed by XRF (Phillips MAGIX PRO Model 2440),with relative standard deviations <3%. For rare earth elements(REEs), HFSE and other trace elements, powders were dissolved inreagent grade HF and HNO3 in Savillex screw top vessels, using theprocedure of Manikyamba et al. (2012), and determined by ICP-MS(Perkin Elmer SCIEX ELAN DRC II) at the National GeophysicalResearch Institute (NGRI), Hyderabad. Certified reference materialsJB-2 and BHVO-1 were run as standards along with the samplesgiven basaltic compositions of major, trace elements and REE. Theanalyses and RSD values of JB-2 and BHVO-1 are given in Table S1.

Fig. 1. (A) Geological map of Godavari Triple Junction (GTJ) showing the location of Rajahmundry Trap basalts (RTB) with respect to Godavari Rift, K-G Basin and Eastern GhatMobile Belt (EGMB). Inset map shows the areal extent of Deccan Traps and RTB in Peninsular India (after Self et al., 2008). (B) Generalized geological map of the Rajahmundry Trapbasalts showing distribution of three lava flows with associated inter- and infratrappean sediments.

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Fig. 3. Photomicrographs showing (A) clustered plagioclase phenocrysts formingglomeroporphyritic texture; zoning is observed in a single plagioclase phenocryst and(B) intersertal and intergranular texture in Rajahmundry Trap Basalts (RTB).

Fig. 2. Field photographs of (A) lower, middle and upper flows of RTB separated byIntertrappean I and II, (B) single to multi-storeyed columnar joints in the lower flowand (C) lower flow exhibiting radial jointing pattern.

Table 1Stratigraphic succession of the Rajahmundry Traps.

Formation Lithology Age

Rajahmundry Conglomerate, sandstone,clay and lignite

Eocene/Miocene (Tertiary)

UnconformityRajahmundry

TrapsUpper Trap (basalt) K/T boundaryIntertrappean II (clay)Middle Trap (basalt)Intertrappean I (clay,limestone and marl)Lower Trap (basalt)Unconformity

Beds (TirupatiFormation)

Sandstone, clay and limestone Maastrichtian(late Cretaceous)

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5. Geochemistry

5.1. Major elements

The RTB show SiO2 content ranging from 47.45 to 50.58 wt.%,moderate to high MgO and CaO (6.19e13.12 wt.% and6.85e10.58 wt.% respectively, Table S2). Al2O3 content shows anarrow range between 10.88 and 12.49 wt.% (Table S2) anddistinctly depict the tholeiitic character. The rocks are typicallyenriched in Fe with 7.56e10.29 wt.% FeO. The K2O content rangesfrom 0.05 to 0.30 wt.% and in terms of SiO2 vs. K2O, the Rajah-mundry Trap basalts are low-K sub-alkaline tholeiites (Fig. 4A). TheTiO2 content of RTB ranges from 1.74 to 2.81 wt.%. These are clas-sified as mid-Ti basalts (TiO2 � 2.0 wt.%) and high Ti-basalts(TiO2 � 2.0 wt.%) where 2 wt.% of TiO2 has been considered asthe boundary keeping in view of the compositional range of plume-related basalts around the world erupted in both continental andoceanic environments (Safonova, 2009; Simonov et al., 2014).Accordingly, the mid-Ti basalts of Rajahmundry have TiO2 contentranging from 1.74 to 1.92 wt.%, while the high-Ti basalts have TiO2

content of 2.04e2.81 wt.%. Geochemical parameter used for con-straining magmatic differentiation like Differentiation Index (D.I.)(Thornton and Tuttle, 1960) shows a wide range of variation from39 to 52 which corroborates middle to late stage magma differen-tiation (Cox, 1980; Wilson, 1989). The major element compositionsof RTB are consistent with that of tholeiitic basalts of Deccan Trapsand Ocean Island Basalts (OIB; Hughes, 1982; Sun and McDonough,1989; Table S2). CIPW normative compositions (Table S2) aremarked by the presence of quartz (4.02e9.89 wt.%) and

Fig. 4. (A) SiO2 vs. K2O plot depicting a low-K sub-alkalic nature of Rajahmundry Trap Basalts (RTB). Field boundaries are from Middlemost (1975). (B) Total alkali (Na2O þ K2O) vs.silica (SiO2) diagram (after Le Bas et al., 1986; Le Maitre, 1989) showing the Rajahmundry samples in the field of Basalt. (C) Total alkali (Na2O þ K2O) vs. silica (SiO2) diagram (afterMcDonald and Katsura, 1964) showing the subalkaline composition of RTB and (D) Rajahmundry Trap Basalts (RTB) showing a distinct tholeiitic trend in (Na2O þ K2O)eFeOTe MgO(AFM) diagram (after Irvine and Baragar, 1971).

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hypersthene (16.18e35.25 wt.%). A silica-oversaturated, quartztholeiitic character of the RTB can be adjudged from the normativemineralogy. In the total alkali (Na2O þ K2O) vs. silica (SiO2) dia-grams (Le Bas et al., 1986; Le Maitre, 2002, Fig. 4B and C) thesamples plot in the field of basalt (Fig. 4B) showing a sub-alkalinecomposition (Fig. 4C). These basalts exhibit a distinct tholeiitictrend in the AFM diagram (after Irvine and Baragar, 1971, Fig. 4D).Abundances of major element oxides such as MgO, CaO, Fe2O3, andTiO2 show a negative correlation with increasing D.I. while Al2O3,Na2O and K2O contents showa positive correlationwith D.I. (figuresnot shown).

5.2. Trace elements

The Rajahmundry Trap basalts are characterized by depletion incompatible elements (Ni, Cr), and relative enrichment in incom-patible elements like Large Ion Lithophile Elements (LILE) and LightRare Earth Elements (LREE; Table S2). Ni (74e129 ppm) and Cr(76e235 ppm) concentrations of RTB are lower than that of primarymantle melts (Ni > 200 ppm, Cr > 400 ppm). Sc (36e43 ppm)concentrations point towards crystallization of clinopyroxenephenocrysts which trap sufficient Sc (Albarede, 1995; Albaredeet al., 1997). These basalts have relatively lower Rb(0.9e11.1 ppm) and Sr (235e315 ppm) as compared to OIB (Rb:31 ppm; Sr: 660 ppm) compositions (Table S2). Ba is widely variable

(54e262 ppm) and reaches up to 262 ppmwith respect to 350 ppmin OIB (Table S2). These basalts have relatively lower Nb and Taconcentrations (6.9e15.37 ppm and 0.5e1 ppm respectively) incomparison with that of OIB (Nb: 48 ppm; Ta: 2.7 ppm; Table S2).Primitive mantle-normalized (Sun and McDonough, 1989) multi-element patterns for RTB (Fig. 5) show consistent trace elementcharacters suggesting an overall geochemical coherence among thethree lava flows. The RTB samples depict positive Ba and Thanomalies and distinct negative anomalies at Rb and K with minorto negligible Sr anomalies. The HFSE patterns show positive Nb-Taanomalies. Negative P, Ti and Yb anomalies are also evident onmulti-element diagram. Chondrite normalized REE patterns exhibitpronounced LREE enrichment (Fig. 5), highly fractionated HREEpatterns and minor to negligible Eu anomaly.

6. Petrogenesis

6.1. Crustal contamination

Compositional variations in mantle-derived magmas have beenattributed to variable amounts of contamination by differentcrustal components during their ascent to the surface throughcontinental crust (Hawkesworth et al., 1984; Mahoney, 1988;Carlson, 1991; Hergt et al., 1991; Arndt and Christensen, 1992;Gallagher and Hawkesworth, 1992; Saunders et al., 1992; Arndt

Fig. 5. Primitive mantle-normalized multi-element spider diagram and Chondrite-normalized REE patterns for the Rajahmundry Trap Basalts (RTB) (normalization values are fromSun and McDonough, 1989).

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et al., 1993; Sweeney et al., 1994; Song et al., 2001, 2008). The basaltflows of Rajahmundry Traps have relatively low K2O/P2O5 (<2)having a range of 0.26e1.26. This feature indicates minimuminvolvement of silicic crustal component or wall rock (of granitic

composition) assimilation during their ascent and storage of theflood basalt magmas. The relatively high TiO2/P2O5 (6.74e16.79) forRTB are compatible with an intraplate OIB source, least affected bycontamination from granitic continental crust (Carlson and Hart,

Fig. 6. (A) Plots of (Ce/Sm)N vs. (Yb/Sm)N variations for Rajahmundry basalts in comparison with Madagascan volcanic (after Radhakrishna and Joseph, 2012). The compositions ofaggregated melts produced by different degrees of melting of a spinel lherzolite and garnet lherzolite sources are shown. Details of model calculations are as given in Storey et al.(1997). (B) (La/Sm)N vs. (Tb/Yb)N diagram for Rajahmundry basalts in comparison with Madagascan volcanic rocks (after Radhakrishna and Joseph, 2012). Details of melting curvesand calculations are referred to Melluso et al. (2001).

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1988). The marked depletion of Rb in the studied samples alsosuggests minimum possibility of contamination from continentalcrustal materials. Thompson et al. (1984) considered La/Nb ratio asa suitable index of crustal contamination in magmas and suggestedthat OIB, continental alkali basalts and kimberlites have La/Nb < 1,while that in CFB magmas range from 0.5 to 7. The La/Nb ratios(0.89e1.45) of the RTB are showing a restricted range with respectto that of CFB and this reflects limited crustal contamination ofparent magma (Peate et al., 1999; Song et al., 2001). HFSE ratios aresuitable indicators of crustal contamination in an open magmasystem. The studied basalts have relatively higher Zr/Nb and Th/Nbratios (11e16 and 0.08e0.13 respectively) than those of the OIB (4.2and 0.06 respectively; Hofmann, 1988; Ionov et al., 1997) and low(Nb/La)PM (0.66e1.1) which may be attributed to lower Nb con-centrations compared to typical OIB (Hofmann, 1988; Mahoneyet al., 1993; Safonova et al., 2008; Buslov et al., 2010;Manikyamba and Kerrich, 2011; Simonov et al., 2014). These lowNb contents do not represent the exogeneous contamination oftholeiitic melts by continental crust but reflect on endogenouscontamination caused due to recycling of lithosphere (havingdepleted upper mantle materials) during subduction of oceanicslab into the mantle (Polat et al., 1999; Safonova et al., 2008). LowTh concentrations (0.71e1.58 ppm) along with Th/Ta ratios of RTBspanning from 1.07e1.85 support minimum crustal contamination(Safonova et al., 2008; Lai et al., 2012). The Nb/Th ratio of primitivemantle is 8, whereas in continental crust it is w1.1 (Taylor andMcLennan, 1985; Sun and McDonough, 1989; Rollinson, 1993).Rajahmundry basalts characteristically have Nb/Th > 8 (Nb/Th:8.35 to 13 except one sample having Nb/Th: 7.7) which is consistentwith that of primitive mantle values thereby reflecting minimumcontamination of parent melt by continental crust. Primitivemantle-normalized multi-element patterns of RTB (Fig. 5) markedby positive Ba anomalies (Ba: 54e262 ppm) and distinct Rb troughs(Rb: 0.9e11.1 ppm) imply minimum input from granitic continentalcrust and indicate contamination of the parent magma during itsmigration to the surface by variable amounts of assimilation of Ba-rich Infratrappean and Intertrappean sediments of estuarine toshallow-marine character.

6.2. Mantle melting conditions

Rare-earth element compositions provide important constraintsin understanding the mantle melting conditions because theirrelative abundances in mantle-derived melts are strongly depen-dent on the degree of partial melting and the nature of aluminousphase (spinel or garnet) in the mantle source (Lassiter et al., 1995;Reichow et al., 2005; He et al., 2010). In general, HREE especially Ybis compatible in garnet and has high garnet/melt partition co-efficients, whereas La (LREE), Sm and Gd (MREE) are incompatibleand have low garnet/melt partition coefficients (Irving and Frey,1978; Kelemen, 1990; Rollinson, 1993). La/Yb and Sm/Yb arestrongly fractionated when melting occurs in the garnet stabilityfield and in contrast to this La/Yb is slightly fractionated and Sm/Ybis nearly unfractionated during melting in the spinel peridotitedomain (Yaxley, 2000; Xu et al., 2005; Lai et al., 2012). Gd/Yb andSm/Yb are distinct indicators of the presence of residual garnetduring partial melting. The REE signatures of RTB marked by (La/Yb)N¼ 2.50e3.65, (Sm/Yb)N¼ 2.06e2.66 and (Gd/Yb)N¼ 1.71e2.31(Table S2) with chondrite-normalized REE patterns (Fig. 5) reflectmoderate to high fractionation of HREE and thus suggest that theparental magmas were derived by partial melting of a mantlesource at variable depths extending from spinel to garnet stabilityfields (Safonova et al., 2008; Buslov et al., 2010). Interceptson melting curves on (Ce/Sm)N vs. (Yb/Sm)N diagram suggestthat these basalts resemble with the tholeiitic and transitionalseries of volcanic rocks from the Mailaka and Bemaraha areas ofcentralewestern Madagascar (Radhakrishna and Joseph, 2012).These are spatially distributed in the region between spinel lher-zolite and garnet lherzolite melts (Fig. 6A). Similar inferences arederived from (La/Sm)N vs. (Tb/Yb)N figure (Fig. 6B). Basaltic lavasare conventionally derived by mantle melting at depths shallowerthan w100 km. It has been suggested that the source regions ofcontinental flood basalt (CFB) magmatism are modified by contri-butions from both continental lithosphere and asthenosphere andthe geochemical processes were occurring over tens of millions ofyears or more (Kürkcüoglu, 2010). In normal mantle, the transitionfrom spinel to garnet peridotite occurs between w60 and 80 km,

Fig. 7. (A) MgO vs. Fe2O3T variations showing a distinct olivine fractionation trend for

Rajahmundry basalts. (B) MgO vs. CaO variations suggesting a plagioclase-clinopyroxene controlled fractional crystallization process for Rajahmundry basalts.

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but in the presence of upwelling mantle plume, this depth may be80e100 km (Sen, 1988; McKenzie and O’Nions, 1991; White andMcKenzie, 1995). Therefore, the mantle melting conditionsderived for the evolution of Rajahmundry Trap basalts suggest thatthese basalts were produced by 3e5% partial melting of a Fe-richmantle regime extending from spinel to garnet peridotite compo-sitional range at depths of 60e100 km.

6.3. Fractional crystallization

The lower, middle and upper flows of Rajahmundry Traps areinequigranular pheonocrystic basalts composed of clinopyroxeneand plagioclase (and minor olivine) phenocrysts which indicatefractional crystallization of the parental magma before eruption.The variation trends of major oxides with respect to progressivedifferentiation of the melt corroborate a magmatic system domi-nated by fractional crystallization. The negative trends observedbetween MgO, CaO, Fe2O3 and D.I. indicate crystallization offerromagnesian phases like clinopyroxene from the melt and thepositive correlation of Al2O3 with D.I. suggests progressive crys-tallization of plagioclase. The overall major oxide compositionssuggest that the mid- to high-Ti basalts of Rajahmundry aregenerated by magmatic fractionation process dominantlycontrolled by crystallization of plagioclase and clinopyroxene.Rajahmundry Trap basalts have MgO content of 6.19e13.12 wt.%and Mg# varying between 29 and 50 which suggest an evolved

chemistry of the flows marked by fractional crystallization ofmagma. Ni (74e129 ppm) and Cr (76e235 ppm) concentrations ofRTB are lower than that of primary mantle melts (Ni > 200 ppm,Cr > 400 ppm) of an olivine dominated source, thereby carryingimplications of widespread fractional crystallization processes andpronouncedmagmatic evolution. The RTB are products of extensivefractional crystallization of clinopyroxene-rich, olivine-poor meltwith plagioclase, clinopyroxene as the dominant crystallizingphases and little or no olivine in the crystallizing mineral assem-blage. This feature can be visualized through the MgO vs. Fe2O3

T

plot (Fig. 7A) where the samples depict distinct olivine fraction-ation trend in the parent magma. The CaOeMgO relationshipsuggests crystal-liquid control by clinopyroxene and plagioclaseduring fractional crystallization processes (Fig. 7B). RTB have rela-tively low Mg# (29e50) attesting to their derivation from a mantlemore Fe-rich than normal MORB-OIB compositions. The evolvednature of these basalts, negative correlation between Mg# andincompatible trace element abundances, negative Sr anomalies andrelatively high Zr contents are in agreement with the observationthat these geochemical variations are a result of magmatic differ-entiation controlled by extensive fractional crystallization over awide range of pressure. Mantle-normalizedmulti-element patternsand chondrite-normalized REE diagram show overall flat patternsfor Sr and Eu respectively. These trace element and REE signaturesof the plagioclase phyric RTB reflect pressure-sensitive crystalliza-tion of plagioclase and variations in melt water content duringcrystallization. It has been envisaged that values of plagioclase/melt-

DREE decreases as the melt H2O content increases and as pressuredrops, while values of plagioclase/meltDSr are sensitive to pressure(Bédard, 2006).

7. Discussion

7.1. Mantle source characters

Primitive mantle-normalized multi-element patterns andchondrite normalized REE patterns (Fig. 5) exhibit higher abun-dances of LILE and LREE of these basalts suggesting that theirparent magma had a mantle source which had experienced suffi-cient enrichment in these elements. Zr/Hf, Zr/Sm and Nb/Ta ratiosagainst respective primitive mantle values of 36, 25 and 17 attest toan enriched mantle source for the derivation of parent magmaproducing RTB. These basalts have Nb (6.9e15.37 ppm) and Zr(109e202 ppm) contents higher than those of the N-MORB(Nb ¼ 2.33 ppm, Zr ¼ 74 ppm) and lower than that of OIB(Nb ¼ 48 ppm, Zr ¼ 280 ppm) implying their generation from anenrichedmantle source (Sun andMcDonough,1989). Trace elementratios like Zr/Nb, La/Nb, Ba/Nb/, Ba/Th, Rb/Nb, K/Nb, Th/Nb, Th/Laand Ba/La maintain distinctive values corresponding to differentmantle sources and provide constraints on the mantle sourcecomponents (Weaver, 1991). The incompatible trace element ratios(Zr/Nb, La/Nb, Ba/Nb/, Ba/Th, Rb/Nb, K/Nb, Th/Nb, Th/La and Ba/La)for Rajahmundry Trap basalts (Table S3) are similar to those of EM Icomponent and account for a parentmagmawhich had an enrichedmantle (EM I) source signature. The most convincing and viableexplanation that accounts for the origin of enriched geochemicalsignatures of mantle plumes is recycling of ancient, subduction-processed, ocean- and continent-derived crustal and lithosphericcomponents into the deep mantle (Hofmann and White, 1982;Sobolev et al., 2007; White, 2010; Cabral et al., 2013). Therefore,ancient subducted and recycled oceanic lithosphere carrying bothoceanic and continental crustal materials seem to have contributedto the source region for plume-sourced OIB magmas and this canalso be expected for CFB magmas as well (Sheth, 2005; Strackeet al., 2005; Garfunkel, 2008). The Ba/Th (46e247), Ba/La

Fig. 8. (A) Th/Ta vs. La/Yb plot (after Condie, 2001) showing the plots of Rajahmundry basalts and the distribution of mantle components. DM: depleted mantle, PM: primitivemantle, PSCL: post-Archaean subcontinental lithosphere, FOZO: focal zone mantle, EM 1 and EM 2: enriched mantle sources, HIMU: high-mu source, UC: upper continental crust,AFC: assimilation-fractional crystallization trajectory. The Rajahmundry basalts show an enriched mantle source character and plot close to FOZO (defining a mixing between EM-HIMU and DM in the plume source) with an affinity towards PSCL. (B) Th/Ta vs. La/Yb plot (after Condie, 2001) in which the Rajahmundry basalts plot proximal to FOZO, close to thefield of Deccan basalts and show distinct affinity towards PSCL. (C) OIB-MORB array in the Nb/Yb vs. Th/Yb diagram (after Pearce, 2008) showing minimum effects of crustalcontamination and subduction in Rajahmundry basalts and the samples cluster in field of Amsterdam-St. Paul OIB. (D) Plots of Ce/Nb vs. Th/Nb for the Rajahmundry Trap Basalts(RTB), Emeishan Continental Flood Basalts (ECFB), depleted mantle (DMM), subduction component (SDC), ocean island basalts (OIB), normal mid-oceanic ridge basalts (N-MORB),enriched mid-oceanic ridge basalts (E-MORB), primitive mantle (PM), and the compositions of upper continental crust and bulk continental crust are from Saunders et al. (1988,1991). Data for Iceland plume are from Hemmond et al. (1993). Fields for arcs are from Saunders et al. (1991). Global subducting sediment composition (GLOSS) after Plank andLangmuir (1998).

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(3.96e28.51) and Th/Nb (0.08e0.13) ratios of RTB are consistentwith a source carrying signatures of EM I which supports thecontention of source enrichment by oceanic crust and lithosphericcomponents recycled through ancient subduction processes(Weaver, 1991; Song et al., 2001). This conjecture is supported bythe La/Yb vs. Th/Ta plot (Fig. 8A; after Condie, 1997) where theRajahmundry Trap basalts belong to the FOZO (focal zone mantle)component mantle source. FOZO is referred as a plume componentlocated in the lower mantle and commonly present in OIB magmas(Condie, 2001). Geochemical imprints like K/Na (0.03e0.22), K/La(43e169), K/Ti (0.04e0.16), K/Nb (50e245) and CaO/Al2O3

(0.59e0.89) suggest an OIB-like enriched mantle source for RTB. Inthe La/Yb vs. Th/Ta diagram (Fig. 8A) the Rajahmundry samples plotclose to the field of Deccan basalts and point towards a strong FOZOcomponent in their plume source. The proximity of the Rajah-mundry samples to the FOZO and PSCL (post-Archaean subconti-nental lithosphere) in La/Yb vs. Th/Ta plots (Fig. 8A and B) indicatesmixing between asthenospheric and lithospheric mantle compo-nents thereby reflecting significant contribution from subconti-nental lithosphere (Hart et al., 1992; Hauri et al., 1994) into plume-

derived melts. The Rajahmundry basalts fall within the MORB-OIBarray in Th/Yb vs. Nb/Yb diagram (Fig. 8C; Pearce, 2008) and theplots are clustered in a trend consistent with the fields ofAmsterdam-St.Paul OIB basalts, Reunion and Mauritius lavas. In theTh/Nb vs. Ce/Nb diagram (Fig. 8D; Saunders et al., 1988) the RTBsamples plot close to the fields of OIB and Emeishan CFB and liebetween a recycled residual slab and a recycled subduction derivedcomponent. Low (Nb/La)PM ranging from 0.66 to 1.1 also supportsthe role of recycled residual slab component in the mantle source(Safonova et al., 2008). An OIB-like mantle enriched by ancientsubducted and recycled oceanic crust gave rise to a source with anEM I signature that eventually supplied the magma parental to theRajahmundry basalts. The mantle source enrichment processeswere dominantly controlled by input from ancient pelagic sedi-ments derived from subducted slabs (retaining HFSE such as Nband Ta) that mixed with the OIB source region in the lower mantleand imparted distinct HFSE enrichment to the source. Nb/U ratio isnot affected by fractional crystallization or partial melting and re-mains constant in MORB and OIB (Nb/U ¼ 47 � 10) reflectingsimilar values in depleted and enriched mantle reservoirs (Taylor

Fig. 9. (A) Zr vs. Zr/Y tectonic discrimination discrimination diagram (after Pearce andNorry, 1979) showing the plots of Rajahmundry basalts in the field of within platebasalts (WPB). (B) Rajahmundry samples displaying an E-MORB like intraplate tectonicaffinity in terms of Hf/3eTheTa compositional variations (after Wood, 1980). A: N-MORB, B: E-MORB, C: WPB, and D: Supra Subduction Zone (SSZ).

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and McLennan, 1985). Nb/U ratios (14e45) of RTB are lower thanthat of MORB and OIB and this particular feature reflects theaddition of U back to the deep plume sources by recycling of ancientsubducted crustal components (Plank and Langmuir, 1998; Condie,2001).

The RTB shows enrichment in incompatible elements and pos-itive Nb anomalies in the multi-element patterns which are char-acteristic features of plume-derived basalts of both oceanic andcontinental settings (Lightfoot et al., 1993; Wooden et al., 1993;Reichow et al., 2005; Xu et al., 2007; Safonova and Santosh, 2014;Simonov et al., 2014). Zr/Ba ratio has been considered as an effec-tive parameter to distinguish lithospheric sources (Zr/Ba: 0.3e0.5)from asthenospheric sources of parent melt (Zr/Ba: >0.5; Menzieset al., 1991; Kürkcüoglu, 2010). The Zr/Ba ratios of RTB rangingfrom 0.51 to 3.24 and Zr/Hf ratios varying between 37 and 41 clearlyindicate involvement of asthenospheric mantle sources in themelting process. Trace element ratios such as Zr/Nb, Zr/Y, Nb/Yprovide viable petrogenetic clues to trace the plume signature inthe genesis of Rajahmundry basalts. It has been suggested thatplume derived basalts have lower Zr/Nb ratios in comparison withN-MORB (Zr/Nb: >301). A relatively lower range of Zr/Nb ratios(11e16) of Rajahmundry samples suggest a plume origin for theparental magma.

Flood basalt magma composition is modified by the composi-tion of the plume source and the processes associated with meltingand migration of melt to the surface. The continental lithosphericmantle and continental crust play important role in the genesis andevolution of CFB magmas (Song et al., 2008). The geochemicalcharacteristics of RTB show evidence of minimum contaminationby granitic continental crust during ascent of magma. Therefore,the importance of continental lithosphere in the generation ofRajahmundry basalts needs to be assessed. The conjunction of lowNb/Ta with high Zr/Hf and Zr/Sm ratios in comparison with prim-itive mantle values (17, 36 and 25 respectively) accounts for hy-drous metasomatism of the mantle indicating an interactionbetween an upwelling plume head and a LILE-LREE enriched SCLMmetasomatized by ancient subduction processes. The higher Th/Ybvalues and its relationship with Nb/Yb (Fig. 8C) provide evidence oflithospheric involvement. The plumeelithosphere interaction inthe formation of RTB can be explained by the high melt retentionand wallerock interaction process suggested by Green and Falloon(1998) where mantle plumes extract incompatible trace elementsfrom the lithospheric mantle during ascent. The HFSE enrichedmantle plume ascended from the lower mantle and interacted withthe SCLM causing LILE and LREE enrichment. However, it has to beconsidered that the subduction-metasomatized, LILE-LREEenriched continental lithospheric mantle is not the only source ofthe Rajahmundry basalts that erupted in continental intraplatesettings. Rather, integrated petrological and geochemical attributessuggest that an interaction between ascending plume carrying anenriched mantle (EM I) signature and the continental lithosphericmantle enriched by ancient subduction processes provides a po-tential magma source for the generation of Rajahmundry basalts.The plume source contributes the enriched mantle (EM I) signatureand the continental lithospheric mantle imparts the LILE and LREEabundances into the parent magma which was derived by 3e5%partial melting of mantle in the compositional range of spinel togarnet peridotite at depths between 60 and 100 km. Subsequentpolybaric fractional crystallization of the melt generated theRajahmundry basalts.

7.2. Evaluation of tectonic setting

Basaltic magmas are known to be emplaced in a variety of tec-tonic settings including intraplate continental or oceanic

environments, intraplate rift zone settings, fast and slow spreadingmid-oceanic ridges, island arcs, and back-arc basins (Pearce andCann, 1973; Pearce and Norry, 1979; Pearce, 2008). The RTB aremid- to high-Ti basalts (TiO2>1.5 wt.%) having Al2O3/TiO2 rangingfrom 3.88 to 6.83 compared with island arc basalts (15e25) andMORB (10e15) which suggests their generation in an intraplatecontinental tectonic setting (Regelous et al., 2003; Manikyambaet al., 2004; Safonova, 2009). Incompatible trace element abun-dances and HFSE ratios serve as suitable parameters to discriminatethe tectonic environment for the eruption of basaltic magmas. TheRajamundry basalts cluster in the field of within plate basalts(WPB) and exhibit E-MORB affinity in terms of Hf/3eTheTa rela-tionship (Fig. 9). Incompatible trace element abundances of RTB(Fig. 5) exhibit positive Th, negative K and Ti anomalies which areconformable with their generation in rift-controlled, intra-continental tectonic setting. Therefore, the geochemical attributesof RTB provide evidence for their in situ intrabasinal eruptionthrough fault-controlled fissures and this observation fits into theregional geological framework of Pangidi-Rajahmundry Basin inthe east coast of India.

Two different schools of opinions exist for the origin andemplacement of RTB; one suggesting long-distance transportationof lava flows from Deccan Traps of western India to the east coastalong Cretaceous palaeovalleys either through Krishna or Godavaririvers (Baksi et al., 1994; Jay and Widdowson, 2008) and the otherview supporting intrabasinal eruption of lavas through fault-controlled fissures in an extensional tectonic milieu (Nageswara

Fig. 10. A schematic model showing the interaction between the plume and lithospheric mantle followed by fault-controlled intrabasinal eruption of Rajahmundry Trap Basalts(RTB).

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Rao et al., 2008; Lakshminarayana et al., 2010). The hypothesis oflong-distance lava transportation along palaeovalleys has alsocorrelated RTB with Deccan Traps of Kolhapur Formation in thewestern India. However, critical evaluation of palaeotectonicreconstruction and paleogeographic setting (Lakshminarayanaet al., 2010) suggests Mesozoic uplift of the Eastern Ghat mobilebelt (EGMB). Consequent change in palaeodrainage in the K-G Ba-sin, fault-related tectonic movements in the Godavari rift andassociated shifts in paleocurrent directions of Cretaceous sedi-mentation do not offer any evidence for the existence of a long-distance Cretaceous palaeo- valley connecting western India tothe east coast. Baksi and Brahmam (1985) proposed that theRajahmundry Traps extruded through local faults and rifts and theywere coeval with the main episode of Deccan volcanism (65 Ma).However, Baksi (1994) suggested a marginally younger 64.0 � 0.4Ma age for RTB in comparison with average age for Deccan volca-nism (65.5 � 0.5 Ma). Long-distance transportation of lava flowsfromwestern Deccan to the east coast would result in considerablecrustal contamination of the lavas. However, the Ba contents(54e262 ppm) and Nb/Th (8e13) ratios for the three lava flows ofRTB suggest (i) minimum contamination of plume-derivedmelts bygranitic continental crust and (ii) assimilation of Ba-rich estuarineto shallow-marine sediments of Infra- and Intertraps by the lavaflows. No lateral variation of bulk rock chemistry, which is apossible consequence of long-distance flows, is observed in thestudied lava flows which again indicate that these are not eastwardextension of Deccan Trap lavas of Western Ghats.

Venkayya (1949) and Pascoe (1950) reported aw10e30 m thicklava flow separated from two flows of variable thickness by aw1e4 m thick intertrappean bed consisting of limestone and marl.Drill cores studies of basalt from southwest and south of Rajah-mundry Traps and of interetrappean sediments recovered at Nar-asapur (70 km south of Rajahmundry) suggest that three basalticlava flows occur at depths of w3.3 km. These lava flows initiallycovered larger areas and appear to have formed in a subaqueous

environment during late Masstrichtian (Govindan, 1981). The d18Ovalues (6.3e7.3&) for RTB are not resulted from crustal contami-nation and have been attributed to interaction of basalt withshallow-marine water (Pascoe, 1950; Baksi et al., 1994). These ob-servations support the present study of the RTB from the Gow-ripatnam and Duddukuru quarries comprising lower, middle andupper flows separated by intertrappeans I and II. The lower flow ofRTB erupted over Infratrappean beds of sandstone, clay and lime-stone representing the late Cretaceous Tirupati Formation. Thephysical volcanological features like radial jointing, rootless cones,brecciated fragments and presence of fossiliferous limestone andmarl blocks suggest eruption of the lower flow as hydrovolcanicexplosion in a shallowmarine environment. Radial jointing pattern(Fig. 2C) in the lower flow gives rise to rosettes which depictdistortion in the cooling isotherm due to percolating water throughcracks and fractures (Bondre et al., 2004, 2006; Duraiswami et al.,2004; Jay, 2005). Patches of limestone occurring in the lower partof the middle flow and absence of characteristic volcanologicalfeatures reflect a relatively quiet mode of eruption over inter-trappean I in a shallowmarine to estuarine environment. The upperflow of RTB erupted over intertrappean II is predominantly made ofred clay/red bole.

A schematic diagram (Fig.10) illustrates the lateMesozoiceearlyCenozoic faults and subsequent basin formation along the eastcoast of India. The Mailaram high (Triassic) was an uplifted blockand a catchment area for the Cretaceous fan delta sediments alongthe east coast of India (Lakshminarayana, 2002). Extensional tec-tonic activities along this Mailaram high gave rise to the Dam-mapeta (Jurassic), Raghavapuram (Cretaceous) and Pangidi-Rajahmundry (CretaceouseTertiary) basins (Fig. 10). The west-ward marine transgression during Maastrichtian (Infratrappeanbeds at Duddukuru) was delimited by the fault controlled EGMBridges (Fig. 10). There were no palaeovalleys linking the westernIndia to the east coast during Cretaceous. The RTB lavas eruptedthrough fault controlled fissures in the Pangidi-Rajahmundry Basin

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(Fig. 10) during CretaceouseTertiary. The present day Krishna andGodavari valleys linking the western India to east coast came intoexistence during Miocene (Krishnan, 1968; Ramakrishnan andVaidyanadhan, 2008). Therefore, evaluation of tectonic settingand emplacement conditions for RTB in terms of regional geologicalframework suggests fault-controlled in situ eruptions in an intra-basinal setting.

7.3. Comparison with Deccan Trap Basalts

The Rajahmundry Trap basalts have relatively higher MgOcontents (6.19e13.12 wt.%) and lower Zr (109e202 ppm) than thatof Deccan Trap Basalts from Dhanu-Nasik-Igatpuri (MgO:4.83e5.55 wt.%; Zr: 152e230 ppm), Indore-Khargaon (MgO:3.79e5.8 wt.%; Zr: 155e277 ppm), Toranmal (MgO: 2.98e7.11 wt.%;Zr: 82e238 ppm), Bijasan Ghat section (MgO: 5.64e7.09 wt.%;Zr:119e167 ppm) and Panna-Jabalpur-Seoni-Nagpur (MgO:4.34e6.3 wt.%; Zr: 111e250 ppm) (Mahoney et al., 2000; Shethet al., 2004; Chatterjee and Bhattacharji, 2008; Shrivastava et al.,2008) which suggest that the RTB shows much lesser degree ofcrustal contamination than that suffered by the Deccan basalts.Further, the granitic continental crust served as one of the majorcontaminants of Deccan lavas during their migration through crust.However, for the Rajahmundry lava flows, the shallow-marine toestuarine infratrappean and intertrappean sediments contami-nated the rising magma. Fractional crystallization has been sug-gested as an important differentiation process operated during thepetrogenetic evolution of the continental flood basalt magmas asobserved for basaltic lava flows of Deccan Traps from WesternGhats section (Mahoney, 1988; Melluso et al., 2004, 2006); BijasanGhat section of Satpura Range (Sheth et al., 2004), Toranmal(Mahoney et al., 2000), Jabalpur and Seoni areas (Shrivastava et al.,2008; Kumar and Shrivastava, 2009), lava flows of Indore-Khargaon, Mhow-Chikaldara (Chatterjee and Bhattacharji, 2008)and Emeishan flood basalts of China (Song et al., 2006, 2008; Laiet al., 2012), flood basalts of Parana, Brazil (Hawkesworth et al.,1992), Wrangellia flood basalts, North America (Lassiter et al.,1995). The MgO contents (6.2e13.12 wt.%) of RTB show a rela-tively higher range, while Mg# values (29e50) are consistent withthat of Deccan lava flows from Dhanu-Nasik-Igatpuri (MgO:4.83e5.55 wt.%; Mg#: 42e47), Indore-Khargaon (MgO:3.79e5.8 wt.%; Mg#: 39e51), Toranmal (MgO: 2.98e7.11 wt.%;Mg#: 32e60), Bijasan Ghat section (MgO: 5.64e7.09 wt.%; Mg#:48e53) and Panna-Jabalpur-Seoni-Nagpur (MgO: 4.34e6.3 wt.%;Mg#: 39e52) indicating a differentiated and evolved chemistrymarked by extensive fractional crystallization of parent magma.

It has been suggested that continental flood basalt (CFB)magmas are products of mantle plume activity and they represent aspectacular manifestation of the Earth’s internal activity in terms of(i) rising of low viscosity, hot mantle material from the core-mantleboundary in the form of a plume, (ii) decompression melting of theplume-head and interaction between plume-derived melts andsub-continental lithospheric mantle (SCLM), (iii) impingement andincubation of plume-head at the base of continental lithosphereand magmatic underplating at the lithospheric base, (iv) partialmelting of magma modified by SCLM and plume components car-rying enriched mantle characters, (v) magmatic differentiation andpolybaric fractional crystallization of magma, and (vi) eruption ofFe-rich, tholeiitic flood basalts through reactivated pre-existing riftsystems or newly generated rifts and fractures initiated by up-welling plume-head (Campbell and Griffiths, 1990; Turner andHawkesworth, 1995; Silver et al., 2006; Garfunkel, 2008). MajorCFB provinces of the world, e.g. Siberia (Lightfoot et al., 1993),British Tertiary Volcanic Province (Thompson and Morrison, 1988),Ethiopia (Thompson et al., 1983), Parana-Etendeka (Gibson et al.,

1997), Emeishan (Song et al., 2008) and Deccan (Mahoney, 1988)preserve geochemical signatures of several contributing sourceslike plume, asthenosphere, SCLM and continental crust that playedsignificant role in their origin and evolution. The geochemical sig-natures of RTB suggest that the magma generation processes aresimilar to that of Deccan Trap basalts in terms of plume and lith-ospheric mantle involvement. However, the Deccan lavas weredominantly contaminated by upper continental granitic crust,while the RTB lavas primarily assimilated infra- and inter-trappeansediments.

Geochemical and tectonic interpretations suggest that theRajahmundry Trap basalts were formed by intrabasinal volcanismthrough fault-controlled fissure eruptions in continental intraplatesetting and were associated with upwelling plume activity, conti-nental rifting, break-up and drifting as generally observed in Con-tinental Flood Basalt (CFB) magmatism (Sheth et al., 2009;Vanderkluysen et al., 2011). Out of two possibilities regarding thespatial and temporal correlation with Deccan Traps, the presentstudy is in conformity with contemporaneous in situ eruption ofRTB lava flows in an intrabasinal setting with geochemical char-acteristics resembling that of Deccan lavas, except the role ofcontamination by granitic continental crust which is minimum forRTB compared to Deccan Traps, and does not accord with the long-distance transportation of lava flows along palaeochannels. Thus, ina broader perspective, it can be inferred that during the Cretaceous,decompression melting of rising Reunion plume-head (related to66e65 Ma Deccan volcanism) may have supplied thermal energyand interacted with the lithospheric mantle for producing Rajah-mundry basalts. Extensional episodes related to Reunion plume-impingement beneath Indian continental lithosphere resulted intorifting and fracturing during the CretaceouseTertiary (K/T bound-ary) transition which generated NWeSE and NEeSW regionalfaults. These fault systems provided pathways for the outpouring ofbasaltic lava flows that flooded the K-G Basin and gave rise to theRTB.

8. Conclusions

(1) The lower, middle and upper lava flows of RTB represent threedistinct phases of lava emplacement; each episode of lavaeruption was punctuated by the deposition of intertrappean Iand intertrappean II. The lower and middle flows were formedby hydromagmatic eruptions during marine transgression in ashallow-marine to estuarine environment, whereas the upperflow erupted during a phase of marine regression.

(2) The lava flows of RTB are three-phenocryst basalts produced by3e5% melting of the mantle source at variable depths fromspinel to garnet peridotite compositional range.

(3) The Rajahmundry Trap Basalts (RTB) show geochemical con-formity with a mantle plume source having EM I signature andtheir petrogenetic evolution is marked by contributions fromplume-derived melts and lithospheric mantle.

(4) The RTB are analogous to Deccan Trap Basalts in terms ofpetrography, geochemical attributes, plume-related enrichedmantle source characters and petrogenetic processes includingmantle melting conditions and fractional crystallization of theparent magma, except their minimum contamination bygranitic continental crust and prominent input from shallow-marine to estuarine Infra- and Inter-trappean sediments.

(5) RTB show no possibility of being southward extension ofDeccan lava flows. The regional tectonic implications andassociated geochemical signatures of RTB do not conform totheir emplacement as long-distance, intracanyon flows ofDeccan Traps and point towards fault-controlled, in situ erup-tions of RTB in an intrabasinal tectonic setting.

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Acknowledgements

The authors are grateful to Prof. Mrinal K. Sen, former Director,NGRI for permission to publish this paper. The authors thank Dr. Y.J.Bhaskar Rao, Acting Director, NGRI for his kind support andencouragement. MS acknowledges 1000 Talents Programme of theChinese Government. The authors are thankful Dr. Sanghoon Kwonfor his editorial handling and valuable suggestions. We are gratefulto Dr. Inna Safonova for many constructive and thought-provokingsuggestions which have improved the quality of the manuscript. Ananonymous journal reviewer is also thanked for critical comments.CM acknowledges CSIR for providing the funds to NGRI to carry outthis research work in MIP-6201-28 (CM). We thank Ms. Lily Wangand Ms. Fei Gao for their editorial assistance. Drs. Keshav Krishnaand Sawant are thanked for providing the analytical facilities. Dr.Tarun C. Khanna and Mr. K. Raju are thanked for their help duringthe field work.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.gsf.2014.05.003.

References

Albarede, F., 1995. Introduction to Geochemical Modeling. Cambridge UniversityPress, London, p. 543.

Albarede, F., Luais, B., Fitton, G., Semet, M., Kaminski, E., Upton, B.G.J., Bachelery, P.,Cheminee, J.-L., 1997. The Geochemical regimes of Piton de la Fournaise Volcano(Réunion) during the last 530000 years. Journal of Petrology 38, 171e201.

Allegre, C.J., Birck, J.L., Capmas, F., Courtillot, V., 1999. Age of the Deccan Traps using187Re-187Os systematic. Earth and Planetary Science Letters 170, 197e204.

Arndt, N.T., Christensen, U.R., 1992. The role of lithospheric mantle in continentalflood volcanism: thermal and geochemical constraints. Journal of GeophysicalResearch 97, 10967e10981.

Arndt, N.T., Czamanske, G.K., Wooden, J.L., Federenko, V.A., 1993. Mantle and crustalcontributions to continental flood volcanism. Tectonophysics 233, 39e52.

Baksi, A.K., Byerly, G.R., Chan, L.-H., Farrar, E., 1994. Intracanyon flows in the Deccanprovince, India? Case history of the Rajahmundry Traps. Geology 22, 605e608.

Baksi, A.K., Brahmam, N.K., 1985. The Rajahmundry Traps, Andhra Pradesh, India:Data on Their Age, Geochemistry and Tectonic Framework of Eruption. Abstract,EOS Transactions, American Geophysical Union 66, p. 1145.

Baksi, A.K., 1994. Geochronological studies on whole-rock basalts from the DeccanTraps, India: evaluation of the timing of volcanism relative to the K-T boundary.Earth and Planetary Science Letters 121, 43e56.

Baksi, A.K., 2001. The RTB, Andhra Pradesh: evaluation of their petrogenesis relativeto the Deccan Traps. Journal of Earth System Science 110, 397e407.

Bédard, J.H., 2006. Trace element partitioning in plagioclase feldspar. Geochimica etCosmochimica Acta 70, 3717e3742.

Bondre, N.R., Duraiswami, R.A., Dole, G., 2004. Morphology and emplacement offlows from the Deccan Volcanic Province. India. Bulletin of Volcanology 66,29e45.

Bondre, N.R., Hart, W.K., Sheth, H.C., 2006. Geology and geochemistry of the San-gamner mafic dike swarm, Western Deccan Volcanic Province, India: implica-tions for regional stratigraphy. Journal of Geology 114, 155e170.

Buslov, M.M., Safonova, I.Yu, Fedoseev, G.S., Reichow, M., Davies, C., Babin, G.A.,2010. Permo-Triassic plume magmatism of the Kuznetsk Basin, Central Asia:geology, geochronology and geochemistry. Russian Geology and Geophysics 51,901e916.

Cabral, R.A., Jackson, M.G., Rose-Koga, E.F., Koga, K.T., Whitehouse, M.J.,Antonelli, M.A., Farquhar, J., Day, J.M.D., Hauri, E.H., 2013. Anomalous sulphurisotopes in plume lavas reveal deep mantle storage of Archaean crust. Nature496, 490e494.

Campbell, I.H., Griffiths, R.W., 1990. Implications of mantle plume structure for theevolution of flood basalts. Earth and Planetary Science Letters 99, 79e93.

Carlson, R.W., 1991. Physical and chemical evidence on the cause and sourcecharacteristics of flood-basalt volcanism. Australian Journal of Earth Science 38,525e544.

Carlson, R.W., Hart, W.K., 1988. Flood Basalt volcanism in the Northwestern UnitedStates. In: Macdougall, J.D. (Ed.), Continental Flood Basalts. Kluwer AcademicPublication, Dordrecht, pp. 35e61.

Chatterjee, N., Bhattacharji, S., 2008. Trace element variations in Deccan basalts:roles of mantle melting, fractional crystallization and crustal assimilation.Journal of Geological Society of India 71, 171e188.

Condie, K.C., 1997. Sources of Proterozoic mafic dyke swarms: constraints from Th/Ta and La/Yb ratios. Precambrian Research 81, 3e14.

Condie, K.C., 2001. Mantle Plumes and Their Record in Earth History. CambridgeUniversity Press, London, 305pp.

Cox, K.G., 1980. A model for flood basalt volcanism. Journal of Petrology 21,629e650.

Duraiswami, R.A., Bondre, N.R., Dole, G., 2004. Possible lava tube system in ahummocky lava flow at Daeud, western Deccan Volcanic Province, India. Jour-nal of Earth System Science 113, 819e829.

Gallagher, K., Hawkesworth, C.J., 1992. Dehydration melting and generation ofcontinental flood-basalts. Nature 358, 57e59.

Ganguly, S., Ray, J., Koeberl, C., Ntaflos, T., Banerjee, M., 2012. Mineral chemistry oflava flows from Linga area of the Eastern Deccan Volcanic Province, India.Journal of Earth System Science 121, 91e108.

Garfunkel, Z., 2008. Formation of continental flood volcanism d The perspective ofsetting of melting. Lithos 100, 49e65.

Geological Society of India, 1996. Geological Map of India.Gibson, S.A., Thompson, R.N., Weska, R.K., Dickin, A.P., Leonardos, O.H., 1997. Late-

Cretaceous rift-related upwelling and melting of the Trindade starting mantleplume head beneath western Brazil. Contributions to Mineralogy and Petrology126, 303e314.

Govindan, A., 1981. Foraminifera from the Infra- and Inter-Trappean SubsurfaceSediments of Narsapur Well-I and the Age of the ‘Deccan’ Trap Flows. IndianColloquiuumonMicroalaeontologyand Stratigraphy 9th Proceedings, pp. 81e93.

Green, D.H., Falloon, T.J., 1998. A Ringwood concept and its current expression. In:Jackson, I. (Ed.), The Earth’s MantledComposition, Structure, and Evolution.Cambridge University Press, Cambridge, UK, pp. 311e381.

Hart, S.R., Hauri, E.H., Oschmann, L.A., Whitehead, J.A., 1992. Mantle plumes andentrainment: isotopic evidence. Science 256, 517e519.

Hauri, E.H., Whitehead, J.A., Hart, S.R., 1994. Fluid dynamic and geochemical aspectsof entrainment in mantle plumes. Journal of Geophysical Research 99,275e300.

Hawkesworth, C.J., Gallagher, K., Kelley, S., Mantovani, M.S.M., Peate, D.W.,Regelous, M., Rogers, N.W., 1992. Parana magmatism and the opening of theSouth Atlantic. In: Storey, B.C., Alabaster, A., Pankhurst, R.J. (Eds.), Magmatismand the Causes of Continental Break-up: Geological Society of London SpecialPublication 68, pp. 221e240.

Hawkesworth, C.J., Rogers, N.W., Vancalsteren, P.W.C., 1984. Mantle enrichmentprocesses. Nature 311, 331e335.

Hemmond, C., Arndt, N.T., Lichtenstein, U., Hofmann, A.W., Oskarsson, N.,Steinthorsson, S., 1993. The heterogeneous Iceland plume: Nd-Sr-O isotope andtrace element constraints. Journal of Geophysical Research 98, 15,833e15,850.

Hergt, J., Peate, D., Hawkesworth, C.J., 1991. The petrogenesis of Mesozoic Gond-wana low-Ti flood basalts. Earth and Planetary Science Letters 105, 134e148.

He, Q., Xiao, L., Balta, B., Gao, R., Chen, J., 2010. Variety and complexity of the Late-Permian Emeishan basalts: Reappraisal of plume-lithosphere interaction pro-cess. Lithos 119, 91e107.

Hofmann, A.W., 1988. Chemical differentiation of the Earth: the relation betweenmantle, continental crust, and oceanic crust. Earth and Planetary Science Letters90, 297e314.

Hofmann, A.W., White, W.M., 1982. Mantle plumes from ancient oceanic crust.Earth and Planetary Science Letters 57, 421e436.

Hughes, C.J., 1982. Igneous Petrology. Elsevier, New York, p. 551.Ionov, D.A., Griffin, W.L., O’Reilly, S.Y., 1997. Volatile-bearing minerals and lithophile

trace elements in the upper mantle. Chemical Geology 141, 153e184.Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification of the

common volcanic rocks. Canadian Journal of Earth Science 8, 523e548.Irving, A.J., Frey, F.A., 1978. Distribution of trace elements between garnet mega-

crysta and host volcanic liquids of kimberlitic to rhyolitic composition. Geo-chimica et Cosmochimica Acta 42, 771e787.

Jay, A.E., 2005. Volcanic Architecture of the Deccan Traps, western Maharastra,India: an Integrated Chemistratigraphic and Paleomagnetic Study. PhD thesissubmitted to Open University, Milton Keynes, 360 pp.

Jay, A.E., Widdowson, M., 2008. Stratigraphy, structure and volcanology of southeastDeccan continental flood basalt province: implication for eruptive extent andvolumes. Journal of Geological Society of London 165, 177e188.

Kelemen, P., 1990. Reaction between ultramafic rock and fractionating basalticliquid I. Phase relations, the origin of calc-alkaline magma series, and the for-mation of discordant dunite. Journal of Petrology 31, 51e98.

Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., 2008. Main Deccan Volcanismphase ends near the K-T boundary: evidence from the Krishna-Godavari Basin,SE India. Earth and Planetary Science Letters 268, 293e311.

Krishnan, M.S., 1968. Geology of India and Burma. CBS Publishers, New Delhi,p. 536.

Kumar, R., Shrivastava, J.P., 2009. Geochemistry of basic dykes from Betul-Jabalpurarea in the Deccan Volcanic Province. Journal Geological Society of India 74,95e107.

Kürkcüoglu, B., 2010. Geochemistry and petrogenesis of basaltic rocks from theDevelida�g volcanic complex, Central Anatolia, Turkey. Journal of Asian EarthSciences 37, 42e51.

Lai, S., Qin, J., Li, Y., Li, S., Santosh, M., 2012. Permian high Ti/Y basalts from theeastern part of the Emeishan Large Igneous Province, southwestern China:petrogenesis and tectonic implications. Journal of Asian Earth Sciences 47,216e230.

Lakshminarayana, G., 1995a. Gondwana sedimentation in the Chintalapudi sub-basin, Godavari valley, Andhra Pradesh. Journal of Geological Society of India46, 375e383.

C. Manikyamba et al. / Geoscience Frontiers 6 (2015) 437e451450

Lakshminarayana, G., 1995b. Fluvial to estuarine transitional depositional setting inthe Cenozoic Rajahmundry Formation, K-G basin, India. Indian Minerals 49,163e176.

Lakshminarayana, G., 1996. Stratigraphy and Structural Framework of the Gond-wana Sediments in the Pranhit-Godavari Valley, Andhra Pradesh. Proceedingsof the IXth International Gondwana symposium 1, pp. 311e330.

Lakshminarayana, G., 1997. Sedimentological evidence for Cretaceous reactivationof the eastern margin of the Cuddapah basin. Journal of Geological Society ofIndia 49, 159e168.

Lakshminarayana, G., 2002. Evolution in basin-fill style during the MesozoicGondwana continental break-up in the Godavari triple junction, SE India.Gondwana Research 5, 227e244.

Lakshminarayana, G., Manikyamba, C., Khanna, T.C., Kanakdande, P.P., Raju, K., 2010.New observations on RTB of the Krishna-Godavari Basin. Journal of GeologicalSociety of India 75, 807e819.

Lakshminarayana, G., Murti, K.S., Rama Rao, M., 1992. Stratigraphy of the UpperGondwana sediments in the Krishna- Godavari coastal tract, Andhra Pradesh.Journal of Geological Society of India 39, 13e27.

Lassiter, J.C., DePaolo, D.J., Mahoney, J.J., 1995. Geochemistry of the Wrangellia FloodBasalt Province: implications for the role of continental and oceanic lithospherein Flood Basalt Genesis. Journal of Petrology 36, 983e1009.

Le Bas, M.J., Le Maitre, R.W., Streckeisen, A., Zanemn, B., 1986. A chemical classifi-cation of volcanic rocks based on the total alkali-silica diagram. Journal ofPetrology 27, 745e750.

Le Maitre, R.W., 1989. A Classification of Igneous Rocks and Glossary of Terms.Blackwell Publication, Oxford, 193pp.

Le Maitre, R.W., 2002. Igneous Rocks: A Classification and Glossary of Terms. Rec-ommendations of the International Union of Geological Sciences Subcommis-sion on the Systematics of Igneous Rocks. Cambridge. Cambridge UniversityPress, London, 236pp.

Lightfoot, P.C., Hawkesworth, C.J., Hergt, J., Naldrett, A.J., Gorbachev, N.S.,Fedorenko, V.A., Doherty, W., 1993. Remobilization of the continental litho-sphere by a mantle plume: major-, trace-element, and Sr-, Nd-, and Pb-isotopeevidence from picritic and tholeiitic lavas of the Noril’sk District, Siberian trap,Russia. Contributions to Mineralogy and Petrology 114, 171e188.

Mahoney, J.J., 1988. Deccan Traps. In: Macdougall, J.D. (Ed.), Continental Flood Ba-salts. Kluwer, Dordrecht, pp. 151e194.

Mahoney, J.J., Storey, M., Duncan, R.A., Spencer, K.J., Pringle, M., 1993. Geochemistryand Geochronology of Leg 130 Basement Lavas: Nature and Origin of theOntong Java Plateau. Proceedings of the Ocean Drilling Programme, ScientificResults 130, pp. 3e22.

Mahoney, J.J., Sheth, H., Chandrashekharam, D., Peng, Z.X., 2000. Geochemistry offlood basalts of the Toranmal section, Northern Deccan Traps, India: implica-tions for regional Deccan stratigraphy. Journal of Petrology 41 (7), 1099e1120.

Malarkodi, N., Keller, G., Fayazudeen, P.J., Mallikarjuna, U.B., 2010. Foraminifera fromthe Early Danian Intertrappean Beds in Rajahmundry Quarries, Andhra Pradesh.Journal of Geological Society of India 75, 851e863.

Manikyamba, C., Kerrich, R., 2011. Geochemistry of alkaline- and associated High-Mg basalts from the 2.7 Ga Penakacherla Terrane, Dharwar Craton, India: anArchean depleted mantle-OIB array. Precambrian Research 188, 104e122.

Manikyamba, C., Kerrich, R., Naqvi, S.M., Rammohan, M., 2004. Geochemical sys-tematics of tholeiitic basalts from the 2.7 Ga Ramgiri-Hungund greenstone belt,Dharwar craton: an intraoceanic arc. Precambrian Research 134, 21e39.

Manikyamba, C., Kerrich, R., Polat, A., Raju, K., Satyanarayanan,M., Krishna, A.K., 2012.Arc Picrite-Potassic Adakitic-Shoshonitic Volcanic Association of the NeoarcheanSigegudda Greenstone Terrane, Western Dharwar Craton: transition from Arcwedge to lithosphere melting. Precambrian Research 212, 207e224.

McDonald, G.A., Katsura, T., 1964. Chemical composition of Hawaiian lavas. Journalof Petrology 5, 82e113.

McKenzie, D., O’Nions, P.K., 1991. Partial melt distribution from inverse of rare earthelement concentrations. Journal of Petrology 32, 1021e1091.

Melluso, L., Morra, V., Brotzu, P., Mahoney, J.J., 2001. The Cretaceous igneousprovince of Madagascar: geochemistry and petrogenesis of lavas and dykesfrom the central-western sector. Journal of Petrology 42, 1249e1278.

Melluso, L., Mahoney, J.J., Dallai, L., 2006. Mantle sources and crustal input asrecorded in high-Mg Deccan Traps basalts of Gujarat (India). Lithos 89, 259e274.

Melluso, L., Barbieri, M., Beccaluva, L., 2004. Chemical evolution, petrogenesis, andregional chemical correlations of the flood basalt sequence in the centralDeccan Traps, India. Journal of Earth System Science 113, 587e603.

Menzies, M.A., Kyle, P.R., Jones, M., Ingram, G., 1991. Enriched and depleted sourcecomponents for tholeiitic and alkaline lavas from Zuni-Bandera, New Mexico:inferences about intraplate processes and stratified lithosphere. Journal ofGeophysical Research 96, 13645e13671.

Middlemost, E.A.K., 1975. The basalt clan. Earth Science Reviews 11, 337e364.Nageswara Rao, P.V., Swaroop, P.C., Ranga Rao, V., 2008. Geochemistry and origin of

basalt flows of Rajahmundry area, Andhra Pradesh, southeast India. GondwanaGeological Magazine 23, 91e102.

Pande, K., Pattanayak, S.K., Subbarao, K.V., Navaneethakrishnan, P., Venkatesan, T.R.,2004. 40Ar-39Ar age of a lava flow from the Bhimashankar Formation, GiravaliGhat, Deccan Traps. Journal of Earth System Science 113, 755e758.

Pascoe, E.H., 1950. A Manual of the Geology of India and Burma. Government ofIndia Press, Calcutta, 2130p.

Pattanayak, S.K., Srivastava, J.P., 1999. Petrography and major-oxide geochemistry ofbasalts from the Eastern Deccan Volcanic Province, India. Geological Society ofIndia Memoir 43, 233e270.

Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applicationsto ophiolite classification and the search for Archaean oceanic crust. Lithos 100,14e48.

Pearce, J.A., Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variationsin volcanic rocks. Contributions to Mineralogy and Petrology 69, 33e47.

Pearce, T.H., Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determinedusing trace element analysis. Earth and Planetary Science Letters 19, 290e300.

Peate, D.W., Hawkesworth, C.J., Marta, M.S.M., Nick, W.R., Turner, S.P., 1999. Petro-genesis and stratigraphy of the high-Ti/Y Urubici magma type in the ParanaFlood Basalt Province and implications for the nature of Dupal-type mantle inthe South Atlantic region. Journal of Petrology 40, 451e473.

Plank, T., Langmuir, C.H., 1998. The chemical composition of subducting sedimentand its consequences for the crust and mantle. Chemical Geology 145,325e394.

Polat, Al, Kerrich, R., Wyman, D., 1999. Geochemical diversity in oceanic komatiitesand basalts from the late Archean Wawa greenstone belts, Superior Province,Canada: trace element and Nd isotope evidence for a heterogeneous mantle.Precambrian Research 94, 139e173.

Radhakrishna, T., Joseph, M., 2012. Geochemistry and paleomagnetism of LateCretaceous mafic dikes in Kerala, southwest coast of India in relation to largeigneous provinces and mantle plumes in the Indian Ocean region. BulletinGeological Society of America 124, 240e255. http://dx.doi.org/10.1130/B30288.1.

Ramakrishnan, M., Vaidyanadhan, R., 2008. Geology of India, Volume I. Geologicalsociety of India, Bangalore, p. 556.

Regelous, M., Hofmann, A.W., Abouchami, W., Galer, S.J.G., 2003. Geochemistry oflavas from the Emperor seamounts, and the geochemical evolution of Hawaiianmagmatism from 85 to 42 Ma. Journal of Petrology 44, 113e140.

Reichow, M.K., Saunders, A.D., White, R.V., Al’Mukhamedov, A.I., Medvedev, A.,Y.,2005. Geochemistry and petrogenesis of basalts from the West Siberian Basin:an extension of the PermoeTriassic Siberian Traps, Russia. Lithos 79, 425e452.

Rollinson, H.R., 1993. Using Geochemical Data: Evaluation, Presentation, Interpre-tation. John Wiley, Chichester, 352pp.

Safonova, I.Yu, 2009. Intraplate magmatism and oceanic plate stratigraphy of thePaleo-Asian and Paleo-Pacific Oceans from 600 to 140 Ma. Ore Geology Reviews35, 137e154.

Safonova, I., Santosh, M., 2014. Accretionary complexes in the Asia-Pacific region:tracing archives of ocean plate statigraphy and tracking mantle plumes.Gondwana Research 25, 126e158.

Safonova, I.Yu, Simonov, V.A., Buslov, M.M., Ota, T., Maruyama, Sh, 2008. Neo-proterozoic basalts of the Paleo-Asian Ocean (Kurai accretion zone, Gorny Altai,Russia): geochemistry, petrogenesis, geodynamics. Russian Geology andGeophysics 49, 254e271.

Saunders, A.D., Norry, M.J., Tarney, J., 1988. Origin of MORB and chemically-depletedmantle reservoirs: trace element constrains. Journal of Petrology (SpecialLithosphere Issue), 415e445.

Saunders, A.D., Norry, M.J., Tarney, J., 1991. Fluid influence on the trace elementcompositions of subduction zone magmas. Philosophical Transactions of theRoyal Society of London Series A335, 337e392.

Saunders, A.D., Storey, M., Kent, R.W., Norry, M.J., 1992. Consequences of plume-lithosphere interactions. In: Storey, B.C., Alabaster, T., Pankhurst, R.J. (Eds.),Magmatism and the Causes of Continental Breakup. Geological Society ofLondon Special Publication 68, pp. 41e60.

Self, S., Jay, A.E., Widdowson, M., Kaszthelyi, L.P., 2008. Correlation of the Deccanand Rajahmundry Trap lavas: are these the longest and largest lava flows onEarth? Journal of Volcanological and Geothermal Research 172, 3e19.

Sen, G., 1988. Possible depth of origin of primary Deccan tholeiitic magma.Geological Society of India Memoir 10, 34e51.

Sen, B., Sabale, A.B., 2011. Flow-types and lava emplacement history of RTB, west ofriver Godavari, Andhra Pradesh. Journal of Geological Society of India 78,457e467.

Sheth, H.C., 2005. Were the Deccan flood basalts derived in part from ancientoceanic crust within the Indian continental lithosphere? Gondwana Research 8,109e127.

Sheth, H.C., Mahoney, J.J., Chandrasekharam, D., 2004. Geochemical stratigraphy offlood basalts of the Bijasan Ghat section, Satpura Range, India. Journal of AsianEarth Sciences 23, 127e139.

Sheth, H.C., Ray, J.S., Ray, R., Vanderkluysen, L., Mahoney, J.J., Kumar, A., Shukla, A.D.,Das, P., Adhikari, S., Jana, B., 2009. Geology and geochemistry of Pachmarhidykes and sills, Satpura Gondwana Basin, central India: problems of dyke-sill-flow correlations in the Deccan Traps. Contributions to Mineralogy andPetrology 158, 357e380.

Shrivastava, J.P., Girdhar, M., Kumar, R., 2008. Petrography, composition andpetrogenesis of Basalts from Chakhla-Delakhari Intrusive Complex (CDIC),Eastern Deccan Volcanic Province, India. In: Srivastava, R.K., Sivaji, Ch, Chala-pathi Rao, N.V. (Eds.), Indian Dykes: Geochemistry, Geophysics and Geochro-nology. Narosa Publishing House, New Delhi, pp. 83e107.

Silver, P.G., Behn, M.D., Kelley, K., Schmitz, M., Savage, B., 2006. Understandingcratonic flood basalts. Earth and Planetary Science Letters 245, 190e201.

Simonov, V.A., Mikolaichuk, A.V., Safonova, I.Yu, Kotlyarov, A.V., Kovyazin, S.V., 2014.Late Paleozoic-Cenozoic intra-plate continental basaltic magmatism of theTienshan-Junggar region in the SW Central Asian Orogenic Belt. GondwanaResearch. http://dx.doi.org/10.1016/j.gr.2014.03.001.

Sobolev, A.V., Hofmann, A.W., Kuzmin, D.V., Yaxley, G.M., Arndt, N.T., Chung, S.L.,Danyushevsky, L.V., Elliott, T., Frey, F.A., Garcia, M.O., Gurenko, A.A.,

C. Manikyamba et al. / Geoscience Frontiers 6 (2015) 437e451 451

Kamenetsky, V.S., Kerr, A.C., Krivolutskaya, N.A., Matvienkov, V.V., Nikogosian, I.K.,Rocholl, A., Sigurdsson, I.A., Sushchevskaya, N.M., Teklay, M., 2007. The amount ofrecycled crust in sources of mantle-derived melts. Science 316, 412e417.

Song, X.-Y., Zhou, M.-F., Hou, Z.-Q., Cao, Z.-M., Wang, Y.-L., Li, Y., 2001. Geochemicalconstraints on the mantle source of the Upper Permian Emeishan ContinentalFlood Basalts, Southwestern China. International Geology Review 43, 213e225.

Song, X.-Y., Qi, H.-W., Robinson, P.T., Zhou, M.-F., Cao, Z.-M., Chen, L.-M., 2008.Melting of the subcontinental lithospheric mantle by the Emeishan mantleplume; evidence from the basal alkaline basalts in Dongchuan, Yunan, South-western China. Lithos 100, 93e111.

Song, X.-Y., Zhou, M.-F., Keays, R.R., Cao, Z.-M., Sun, M., Qi, L., 2006. Geochemistry ofthe Emeishan flood basalts at Yangliuping, Sichuan, SW China: implications forsulphide segregation. Contributions to Mineralogy and Petrology 152, 53e74.

Storey, M., Mahoney, J.J., Saunders, A.D., 1997. Cretaceous basalts in Madagascar andthe transition between plume and continental lithosphere mantle sources. In:Mahoney, J.J., Coffin, M.F. (Eds.), Large Igneous Provinces: Continental Oceanicand Planetary Flood Volcanism. American Geophysical Union GeophysicalMonograph, Washington 100, pp. 95e122.

Stracke, A., Hofmann, A.W., Hart, S.R., 2005. FOZO, HIMU, and the rest of the mantlezoo. Geochemistry, Geophysics, Geosystems 6 (5), Q05007. http://dx.doi.org/10.1029/2004GC000824.

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanicbasalts: implications for mantle composition and processes. In: Saunders, A.D.,Norry, M.J. (Eds.), Magmatism in Ocean Basins. Geological Society of LondonSpecial Publication 42, pp. 313e345.

Sweeney, R.J., Duncan, A.R., Erlank, A.J., 1994. Geochemistry and petrogenesis ofcentral Lebombo basalts of the Karoo igneous province. Journal of Petrology 35,95e125.

Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition andEvolution. Oxford. Blackwell Scientific publications, London, p. 312.

Thompson, R.N., Morrison, M.A., 1988. Asthenospheric and lower-lithosphericmantle contributions to continental extensional magmatism: an examplefrom the British Tertiary Province. Chemical Geology 68, 1e15.

Thompson, R.N., Morrison, M.A., Hendry, G.L., Parry, S.J., 1984. An assessment oftherelative roles of crust and mantle in magma genesis: an elemental approach.Philosophical Transactions of the Royal Society of London A310, 549e590.

Thompson, R.N., Morrison, M.A., Dickin, A.P., Hendry, G.L., 1983. Continental Floodbasalts... arachnids rule OK? In: Hawkesworth, C.J., Norry, M.J. (Eds.), Conti-nental Basalts and Mantle Xenoliths. Shiva Pub., Cambridge, MA, pp. 158e185.

Thornton, C.P., Tuttle, O.F., 1960. Chemistry of igneous rocks: pt. 1, differentiationindex. American Journal of Science 258, 664e684.

Turner, S.P., Hawkesworth, C.J., 1995. The nature of the subcontinental mantle:constraints from the major element compositions of continental flood basalts.Chemical Geology 120, 295e314.

Vanderkluysen, L., Mahoney, J.J., Hooper, P.R., Sheth, H.C., Ray, R., 2011. The feedersystem of the Deccan Traps (India): insights from dike geochemistry. Journal ofPetrology 52, 315e343.

Venkayya, E., 1949. Deccan Trap outliers of the Godavari Districts. Indian Academyof Science Proceedings 29, 431e441.

Weaver, B.L., 1991. The origin of ocean island basalt end member compositions:trace element and isotopic constraints. Earth and Planetary Science Letters 104,381e397.

White, W.M., 2010. Oceanic Island Basalts and Mantle Plumes: the geochemicalperspective. Annual Review of Earth and Planetary Science 38, 133e160.

White, R.S., McKenzie, D., 1995. Mantle plumes and flood basalts. Journal ofGeophysical Research 100, 17543e17585.

Wilson, M., 1989. Igneous Petrogenesis. Unwin Hyman, London, p. 466.Wood, D.A., 1980. The application of a Th-Hf-Ta diagram to problems of tectono-

magmatic classification and to establishing the nature of crustal contaminationof basaltic lavas of the British Tertiary volcanic province. Earth and PlanetaryScience Letters 50, 11e30.

Wooden, J.L., Czamanske, G.K., Fedorenko, V.A., Arndt, N.T., Chauvel, C., Bouse, R.M.,King, B.W., Knight, R.J., Siems, D.F., 1993. Isotopic and trace-element constraintson mantle and crustal contributions to Siberian continental flood basalts,Noril’sk area, Siberia. Geochimica et Cosmochimica Acta 57, 3677e3704.

Xu, J.-F., Suzuki, K., Xu, Y.-G., Mei, H.-J., Li, J., 2007. Os, Pb, and Nd isotopegeochemistry of the Permian Emeishan continental flood basalts: insights intothe source of a large igneous province. Geochimica et Cosmochimica Acta 71,2104e2119.

Xu, Y.-G., Ma, J.-L., Frey, F.A., Feigenson, M.D., Liu, J.-F., 2005. Role of lithosphere-asthenosphere interaction in the genesis of Quaternary alkali and tholeiiticbasalts from Datong, western North China Craton. Chemical Geology 224 (4),247e271.

Yaxley, G.M., 2000. Experimental study of the phase and melting relations of ho-mogeneous basalt þ peridotite mixtures and implications for the petrogenesisof flood basalts. Contributions to Mineralogy and Petrology 139, 326e338.